Sign-constancy of Green’s functions for impulsive nonlocal boundary value problems

We consider the following second order impulsive differential equation with delays: $$ \textstyle\begin{cases} (Lx)(t)\equiv x''(t)+\sum_{j=1}^{p} a_{j}(t) x'(t-\tau _{j}(t)) + \sum_{j=1}^{p} b_{j}(t) x(t-\theta _{j}(t)) = f(t), \quad t \in [0, \omega ], \\ x(t_{k})=\gamma _{k} x(t_{k}-0), \quad\quad x'(t_{k})=\delta _{k} x'(t_{k}-0), \quad k=1,2,\ldots,r. \end{cases} $${(Lx)(t)≡x″(t)+∑j=1paj(t)x′(t−τj(t))+∑j=1pbj(t)x(t−θj(t))=f(t),t∈[0,ω],x(tk)=γkx(tk−0),x′(tk)=δkx′(tk−0),k=1,2,…,r. In this paper we consider sufficient conditions of nonpositivity of Green’s function for impulsive differential equation with nonlocal boundary conditions.